A bis(aminomethyl)cyclohexane is an industrially important compound to be used as a starting material for e.g., epoxy hardeners, polyamides and polyurethanes. A bis(aminomethyl)cyclohexane has two isomers, i.e., a cis-isomer and a trans-isomer, derived from a cyclohexane ring. It is known that the physical properties of a polymer obtained by using a bis(aminomethyl)cyclohexane greatly vary depending upon the ratio of isomers, i.e., the ratio of a cis-isomer and a trans-isomer.
For example, it is known that for a polyamide obtained by using 1,4-bis(aminomethyl)cyclohexane, as the content of a trans-isomer increases, the melting point increases, with the result that the heat resistance increases (Non Patent Literature 1). It is also known that a polyurethane obtained by using 1,4-bis isocyanatomethyl cyclohexane derived from 1,4-bis(aminomethyl)cyclohexane is improved in physical properties required for various applications as the content of a trans-isomer increases (Patent Literature 1).
It is further reported that a polyamide, which is obtained by using 1,3-bis(aminomethyl)cyclohexane, having a high cis-isomer content has high crystallinity; whereas a polyamide having a high trans-isomer content is amorphous (Non Patent Literature 2).
For these reasons, it is extremely important to control the isomer ratio of a bis(aminomethyl)cyclohexane.
Bis(aminomethyl)cyclohexane is produced by a method known in the art. To describe more specifically, a bis(aminomethyl)cyclohexane can be obtained by hydrogenating an aromatic dinitrile in the presence of a catalyst to synthesize a xylylenediamine and nuclear-hydrogenating the xylylenediamine obtained in the presence of a catalyst.
A large number of methods are known in the art for producing a xylylenediamine from an aromatic dinitrile by hydrogenation; for example, a method using a Raney catalyst such a Raney nickel or Raney cobalt is reported (Patent Literature 2).
A large number of methods are also known in the art for producing a bis(aminomethyl)cyclohexane by nuclear hydrogenation of a xylylenediamine. In the nuclear hydrogenation reaction of a xylylenediamine, a cis-isomer is more easily produced than a trans-isomer. Thus, it is generally difficult to selectively synthesize a trans-isomer.
For example, a method using a catalyst having ruthenium immobilized to a carrier is reported (Patent Literature 3); however the proportion of a trans-isomer of a bis(aminomethyl)cyclohexane synthesized by this method is generally 50% or less.
Up to present, an isomerization reaction for obtaining 1,4-bis(aminomethyl)cyclohexane having a high content of a trans-isomer has been proposed. For example, a method for obtaining trans-1,4-bis(aminomethyl)cyclohexane by isomerizing 1,4-bis(aminomethyl)cyclohexane in the presence of a noble metal catalyst such as platinum or ruthenium is reported (Patent Literatures 4-6).
Another method for obtaining trans-1,4-bis(aminomethyl)cyclohexane is reported, in which 1,4-bis(aminomethyl)cyclohexane is derivatized into an aldimine compound and then isomerization is carried out and the aldimine compound is decomposed (Patent Literature 7).
Also, as a method for obtaining 1,4-bis(aminomethyl)cyclohexane having a high content of a trans-isomer, a method of obtaining 1,4-bis(aminomethyl)cyclohexane from starting terephthalic acid via a cyclohexane dicarboxylic acid, is reported (Patent Literature 8).
Furthermore, a method of isomerizing 1,4-bis(aminomethyl)cyclohexane by blending it with a benzylamine compound and an alkali metal, an alkali metal hydride or an alkali metal amide is reported (Patent Literature 9). In this method, it is possible to isomerize a bis(aminomethyl)cyclohexane without passing through a complicated multi-stage process.